Which Parts Should You Add To Your '99 To '02 Cummins First?

Order Of Modifications

The most common parts readers bolt onto their trucks are aftermarket intakes and high-flow exhaust systems designed to increase airflow. Typically, enthusiasts combine those parts with a module or programmer that adds more fuel. Combined, that's about $2,000 worth of components to add to your truck. But what if you don't have $2,000 to spend at one time? Which part should you add first? That's exactly what we set out to uncover in our latest test.

Our guinea pig was an '02 two-wheel-drive Dodge Ram 3500 dualie with a VP44-injected Cummins 24-valve engine, and an NV5600 six-speed manual transmission. The truck was bone-stock-right down to the tires-and had 85,000 miles on the ticker. The results of our testing are intended to provide information about a logical upgrade path for any comparable truck. However, it should be noted that every diesel vehicle will respond differently to modifications.

Scientific Method
The scientific method requires experimentation, and diesel performance is a science these days. The key to accurate testing is limiting the number of variables to isolate each component that you wish to test. Ideally, we'd evaluate each part under exactly the same conditions for hundreds or thousands of miles to minimize anomalies. Still, every effort was made to limit the variables that might affect mileage and power. All dyno pulls were made with the hood open and a fan pushing air through the engine bay to minimize heat soak. The mileage testing was performed on the same 80-mile loop of rural road with the cruise control set at 65 mph for as much of the drive as possible. In addition, the same fuel station, and even the same pump, was used to fuel the truck between mileage runs.

The Criteria
We use this Dodge to regularly tow a fifth-wheel trailer or a car trailer with a Jeep on it. The criteria for parts chosen was that components had to be reasonably priced and had to add more usable horsepower, torque, and mileage without sacrificing reliability. Additionally, the parts had to bolt on with basic handtools over the course of a day. Each part was individually dyno-tested at Imler Diesel Performance on its Mustang dyno in order to determine the added torque and horsepower each item contributed. Then the parts were combined and retested to determine the collective improvements.

Intake System
Factory engineers balance costs and noise reduction with airflow, which results in compromises that leave power on the table. S&B Filters offers an intake for the 24-valve Dodge (P/N 75-5044) that flows 55 percent more than the factory intake, thanks to its cotton gauze filter with deep pleats and a larger overall size with increased surface area. The improved airflow does not come at the expense of filtering, as S&B performs the ISO 5011 Air Filtration Test Standard on all its filters. An S&B intake manifold was added in conjunction with the intake kit. The S&B intake manifold is CNC-machined from cast aluminum and is said to be 45 percent less restrictive than the stock intake manifold. The S&B piece features an O-ring to ensure leak-free performance and is tapped with five 1/8-inch NPT ports for everything from pressure sensors to nitrous nozzles to water-methanol injection.

If you're paying close attention, you will note that we just got done stating that we wanted to limit variables, then we added the S&B intake manifold at the same time as its air intake kit. S&B products are very cost competitive, and we were able to add both the intake and the manifold for less than $500, which is less than the price of just an air intake from many manufacturers. The intake system did not seem to be the most restrictive stock component, but it did provide more than a 1/2-mile increase in fuel mileage on our test loop and lowered EGT. The S&B intake also produced an audible whistle inside the cab, which we consider music, but some might find intrusive.

Performance Tuning
The '99 to '02 Cummins 24-valve engine is the black sheep of B-series engines. It takes more than a fuel plate to add more performance, yet it does not have the sophisticated electronics and high-rail pressure of the later common-rail engines. The Mads Electronics Smarty has made a name for itself as the programmer to have for the common-rail Cummins, so we were curious to see what it could do for a VP44-equipped truck (P/N S-03). The Smarty offers 10 different tunes in addition to individually altering fuel duration, fuel timing, and torque management. The Smarty required no additional boost-fooling device and can be uploaded with or without additional timing, allowing it to be safely stacked with boxes that alter fuel timing. It also downloads and clears diagnostic trouble codes and allows for speed limiter and tire size adjustments.

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| The Smarty was easy to hook up and only took a couple of minutes to load new tunes. There were a myriad of options for fuel duration, fuel timing, and torque management, but we only tested the truck with the stock programming and the Smarty on Level 5 in order to limit the variables.

With so many variables, we could run a whole series of tests with just the Smarty to determine the power and mileage improvements, but for this assignment all testing was done with the Smarty on Level 5 (Soft Catcher with added timing). The Smarty alone produced an extra 140 lb-ft of torque on the dyno. There were trade-offs, though, as this setting produced visible smoke during hard acceleration and actually cost us 1/2 mile per gallon during our mileage loop. The decrease in mileage suggested that the excess fuel was not supported by enough airflow-a theory supported by the increased EGT we experienced with the Smarty.

Exhaust Upgrade
Since it was the most involved installation, we saved the Silverline 4-inch, mandrel-bent, stainless steel exhaust (P/N DS101409) for last. While not the least expensive option on the market, Silverline offers a product that is an excellent value. Silverline uses 409-series stainless steel and welded exhaust hangers to set it apart in a sea of exhaust manufacturers. Our only complaint is the use of C-clamps instead of band clamps, as the C-clamps slightly dented the tubing and will make it difficult to remove in the future.

One of our favorite qualities of the Silverline exhaust was that it was barely louder than the stock system. Straight pipes are great for bragging rights at the dragstrip, but they get old when you're pulling a trailer over mountain passes all day long. With the exhaust installed and the truck back on the dyno, we saw a small bump in power and torque. Where the Silverline exhaust really shined was with the huge reduction in EGT with all the various configurations.

Sum Of The Parts
After a full day on the dyno, our last pulls combined the S&B air intake and manifold, Smarty programmer, and Silverline exhaust together. Surprisingly, the combination made only slightly more peak horsepower than the Smarty alone. Curious as to why we were not seeing more power, Ken Imler immediately suspected our fuel pressure.

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| We made every effort to use the same fuel station and even the same pump for our fuel economy testing. Although testing was performed during several weeks, the weather was relatively consistent across all tests.

The stock lift pump had finally succumbed after a full day of torture on the dyno, only producing a meager 2 psi of fuel pressure. Imler explained that the factory Carter lift pumps are designed to push fuel, but Dodge mounted them on the engine where they are required to pull the fuel from the tank, making failure not a matter of if, but when. Failure of the lift pump often leads to destruction of the injection pump as well, which can cost thousands of dollars to replace. On page 132, we'll walk you through the steps we took to upgrade this Dodge's fuel system with a BD Diesel Flow-Max lift pump to provide enough fuel to support all our new modifications, and we'll return to the dyno to see if more fuel further increases our power numbers.